1. Technical Field
The present invention relates in general to detecting stray magnetic fields in disk drive applications and, in particular, to an improved system, method, and apparatus for protecting a hard disk drive from the potentially harmful effects of stray magnetic fields.
2. Description of the Related Art
Data access and storage systems generally comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to five disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm). Hard disk drives have several different typical standard sizes or formats, including server, desktop, mobile (2.5 and 1.8 inches) and microdrive.
A typical HDD also uses an actuator assembly to move magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is aerodynamically shaped to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk.
A slider is typically formed with an aerodynamic pattern of protrusions on its air bearing surface (ABS) that enables the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each disk and flies just over the disk's surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system.
The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop and settle directly over the desired track.
The emerging market for HDDs is expanding very rapidly as HDDs are used in increasingly diverse environments. Some HDDs are used in places where other magnetic objects are present. The stray magnetic field generated by such magnetic objects can interfere with the normal operation of the HDD if the field is strong enough. External magnetic fields can affect both read and write operations of the magnetic heads in HDDs. Moreover, future HDDs probably will use “perpendicular recording,” which is even more sensitive to external stray magnetic fields than traditional “longitudinal recording.” With longitudinal recording, technology, the magnetization of the disk is in the plane of or parallel to the surface of the disk. However, with perpendicular recording technology, the magnetization is perpendicular to the plane of the surface of the disk. Perpendicular disks have a soft magnetic underlayer that is more sensitive to external stray magnetic fields than traditional, longitudinally recorded disks. Thus, an improved design for at least detecting and/or protecting an HDD from the potentially harmful effects of stray magnetic fields would be desirable, especially as perpendicular disks become more popular.